The present invention relates to torque control tools in general, and, specifically, to a torque control tool which uncouples a driven end of the tool from a drive end of the tool upon application of a predetermined torque in an installation direction, and which remains coupled in a removal direction at torquest higher than the installation torque.
Torque control tools of the type which automatically uncouple a driven section from a drive section are known. Examples of such tools appear in U.S. Pat. Nos. 3,662,628, 3,667,250 and 3,702,546 to Schnepel. U.S. Pat. No. 3,662,628 is typical and will be described. The patentee uses a shaft keyed to a radially extending disc to transmit torque to a driven section of the tool through balls. The balls couple between the driven section and the disc by indexed, semi-spherical pockets in both the disc and the driven section. Springs, such as Belleville springs, act on the disc and apply a compressive force axially of the shaft onto the balls to keep the balls seated in the sockets. When the torque between the driven section and the disc becomes sufficiently great, the balls are forced out of their sockets and the driven section becomes uncoupled from the disc. The spring force can be varied to change the uncoupling torque.
The point at which the driven section becomes uncoupled from the drive section can be considered the uncoupling torque. In the known prior art, the uncoupling torque is the same for both directions of rotation. The tool is typically used in making joints by setting threaded fasteners through the tightening of a nut or bolt on its complement. It is desirable to have removal torque higher than installation torque so that a joint can be broken down without adjustments to the tool or without use of a different tool.
The Schnepel patent also discloses a coupling between the drive shaft and disc which permits relative movement between the two along the axis of the shaft. The stated purpose of this construction permits the shaft to move in response to installer's loading without axially loading the disc.
U.S. Pat. No. 3,727,432 to Eaves et al discloses a torque limiting clutch that uses an inner member coupled to an outer member by balls in radial passages of the inner member. The outer member has axially extending grooves that receive the balls. Viewed in radial cross section normal to the axis of rotation of the Eaves et al device, the grooves on one side have a radius of curvature substantially equal to the radius of the balls and on the opposite side the radius of curvature progressively increases as distance increases away from the portion having circular curvature. Consequently, in the Eaves et al device rotational slippage between the inner and outer member occurs while the balls are in the grooves and before the members uncouple.